Twisted waveguide applicator

ABSTRACT

An apparatus is disclosed having an electromagnetic waveguide energy transmission structure providing applied orthogonally disposed high frequency electric fields disposed around material being processed in one complete traversal. The resultant electric field intensity distribution provides for uniform heating of products having nonuniform cross-sectional configuration. Objects, such as rubber moldings or extrusions, may be uniformly cured by the orthogonal electric field orientation. The apparatus utilizes conveyor mechanisms for continuously feeding strip materials to be treated. The transmission structure may be of a hollow rectangular or circular configuration or a combination of both. To assist in the removal of any vapors or to maintain heating temperature, fluid circulation means are disposed over predetermined zones of the oven energy applicator.

United States Patent 91 Peterson 111 3,715,551 51 Feb. 6, 1973 [54]TWISTED WAVEGUIDE APPLICATOR [75] inventor: Robert A. Peterson, Canton,Mass.

[73] Assignee: Raytheon Company, Lexington,

Mass.

[22] Filed: July 1, 1971 [21] Appl.N0.: 158,919

[52] US. Cl ..219/10.ss [51] Int. Cl. ..H05b 9/06 [58] Field of Search..2l9/l0.55

[56] References Cited UNITED STATES PATENTS 2,7l8,580 9/1955 Shirley..2l9/l0.55 3,528,179 9/1970 Smith ..2l9/l0.55 X

Primary Examiner--J. V. Truhe Assistant Examiner-Hugh D. JaegerAttorneyI-iarold A. Murphy et al.

[57] ABSTRACT An apparatus is disclosed having an electromagneticwaveguide energy transmission structure providing applied orthogonallydisposed high frequency electric fields disposed around material beingprocessed in one complete traversal. The resultant electric fieldintensity distribution provides for uniform heating of products havingnonuniform cross-sectional configuration. Objects, such as rubbermoldings or extrusions, may be uniformly cured by the orthogonalelectric field orientation. The apparatus utilizes conveyor mechanismsfor continuously feeding strip materials to be treated. The transmissionstructure may be of a hollow rectangular or circular configuration or acombination of both. To assist in the removal of any vapors or tomaintain heating temperature, fluid circulation means are disposed overpredetermined zones of the oven energy applicator.

10 Claims, 7 Drawing Figures PATENTEDFEB 6l975 3.715.551

SHEET 2 OF 2 ENERGY INPUT TWISTED WAVEGUIDE APPLICATOR BACKGROUND OF THEINVENTION The invention relates to heating by high frequency electricenergy in the microwave portion of the electromagnetic spectrum andmeans for orienting the electric field distribution to uniformly heat aproduct.

Dielectric heating utilizing energy in the electromagnetic wave spectrumhas found wide acceptance in the processing of nonconductive and poorthermally conductive materials, including foodstuffs, paper, wood,rubber, leather, and other materials. An energy generator of highfrequency waves is the magnetron oscillator of World War II radarsystems fame. The text Microwave Magnetrons, Radiation Laboratory SeriesVol. 6, by G. B. Collins, McGraw-I-Iill Book Company, lnc., 1948,provides a comprehensive description of the construction and operationof such devices. The energy generator operates at frequencies within theallotted Federal Communication Commission frequency band for electronicovens of 915 and 2450 megahertz. Other high frequency energy generatorsinclude vacuum tube oscillators and klystrons. High voltage circuitscarrying many thousands of volts of electrical energy are utilized forthe generator. For the purposes of the present specification, the termmicrowave is defined as the electromagnetic energy radiation in thatportion of the spectrum having wavelengths in the order of approximately 1 meter to 1 millimeter and frequencies in excess of 300megahertz.

In the treatment of various materials the electric field intensitywithin the oven is of paramount importance. Critical alignment of theproduct with relation to the input and output feed structuresand mainoven section is required to provide for the propagation of the energy incertain selected modes, for example, TE, and TE, in rectangular orcircular waveguide structures. A problem arises, however, in thetreatment of nonuniform cross section materials wherein irregularitiesin heating are observed with certain hot spots and faulty curingresulting. In particular, products such as rubber extrusions and tubingin rolls can be advantageously treated with microwave energy if suitabledisposition of the electric fields is provided for uniform heating. In

the treatmentof such rubber products, it is customary forthe curingoperation to be carried out after the complex-shaped extrusions havebeen fabricated.

" Other products having poor thermal conduction characteristics andirregular shapes can also be readily treated with the disclosedmicrowave oven apparatus. Vapors and fumes emitted during the heatingcycle are rapidly removed to enhance the efficient and safe operation ofthe apparatus.

SUMMARYOF THE INVENTION .In accordance with the teachings of the presentinvention, a microwave .oven apparatus is provided for frequencyalternating electric field distribution. A conveyor extends throughoutthe .length of the oven apparatus to transport the products through thecomplete heating cycle. Each end of the oven is provided with a feedstructure having means to prevent the escape of electrical energy fromthe entrance and exit ports of the conveyor. The main oven section may,illustratively, be of a waveguide structure having a rectangular crosssection provides for zone heating having orthogonally oriented electricfield distribution. The first zone provides a field of predeterminedintensity and a second zone provides an electric field orientationrotated with respect to the first zone. In addition, vapors may beremoved by circulating air means which also aid in maintaining thetemperature in the oven during processing. Alignment problems in theorientation of the traversing materials have been substantially reducedby the orthogonal orientation of the high frequency electric fielddistribution.

BRIEF DESCRIPTION OF THE DRAWINGS Details of illustrative embodiments ofthe invention will be readily understood after consideration of thefollowing description and reference to the accompanying drawings,wherein;

FIG. 1 is an elevational view of a conveyerized oven apparatus embodyingthe invention;'

FIG. 2 is a detailed cross-sectional view of the waveguide transmissionstructure of the main oven taken along the line 2-2 in FIG. 1.

FIG. 3 is a detailed cross-sectional view taken along line 33 in FIG.1;

FIG. 4 is a cross-sectional view of an exemplary product of nonuniformcross-sectional area for treatment with the microwave oven apparatus;

FIG. 5 is an elevation view of a portion of an alternative apparatus;

FIG. 6 is an elevation view of a portion of an embodiment oftheinvention having air circulation means;

FIG. 7 is a view partly in section of an alternative embodiment of theinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, the mainsection 2 of the oven apparatus defines the heating enclosure throughwhich the product to be processed is transported. An entrance portcomprises an input feed structure 4 and an exit port by output feedstructure 6. Conveyor mechanism 8 includes belt 10 and a drum and gearactuating mechanism 12 driven by suitable means (not shown)-for the sakeof clarity in understanding the present invention. The entrance and exitstructures provide a hollow passageway and are fabricated of a metallicmaterial with the dimensions selectedto attenuate and substantiallyprevent the escapeof the electrical energy from the open ports. Squarewaveguide.

satisfies this requirement. Alternatively, energy attenuating means suchas, for example, a curtain of -a lossy liquid can be disposed adjacentto the open ports.

foregoing arrangement provides for a symmetrical energy distribution.-In such a structure, the high frequency microwave energy fed into theoven from each end is isolated by circulators 26 and 28 of thewell-known ferrite material configuration. Loads 30 and 32 coupled tothe respective ferrite circulators attenuate and absorb energy directedto this component from opposing ends of the oven apparatus. Theprovision of the dual energy feeding arrangement provides for a moreeven distribution of the heating energy required for operation. Wheredesired, one of the energy sources may be eliminated and the waveguidetransmission bend 24, for example, will be terminated by a metallicshort circuiting member.

Intermediate waveguide transmission structure 34, between the first andsecond zone sections 14 and 22, provides a transition for rotation ofthe high frequency electric field pattern in the manner now to bedescribed. Referring to FIG. 2 the rectangular cross section of thewaveguide section 14, provides parallel opposing narrow walls 14a andbroad walls 14b. Flanges 36 having mounting holes 38 provide for thecoupling of section 14 to adjacent structure 16 and 34. In the microwaveart, the propagation of energy in the transverse electric mode throughuniform hollow conduit'transmission means has a configuration describedin the text Microwave Engineers Handbook, 1966, Horizon. House-MicrowaveInc., at page 23 for the TE mode in rectangular waveguide, and page 24for the TE, mode for circular waveguide. It will be noted that in therectangular transmission line, the electric fields have a varyingintensity pattern between broad walls 14b with the maximum in a centeredarea represented by lines 40. The less intense energy fields,represented by lines 42, are adjacent to narrow sidewalls 14a. Theheating of products having irregular nonuniform shapes, therefore, isuneven if the oven apparatus has only one electric field patternthroughout its length. To circumvent the problems inherent in the priorart, the invention provides for the orientation of the electric fieldpatterns in an orthogonal manner with the electric fields rotated 90 ina second heating zone relative to the electric field orientation in afirst heating zone. Transition section 34, therefore, provides awaveguide twist with the broad walls similar to those designated by thenumeral 14b being rotated to assume a new position indicated by thewalls 34b. In alike manner, the-narrow sidewalls having the designationa in FIG. 2 are now rotated 90 to assume the position indicated by walls34a.

In FIG. 3, the downstream orientation of the applied electric fieldpattern within the waveguide transmission structure after rotation isillustrated. Narrow sidewalls 22a are now'disposed in an orthogonalmanner with respect to the narrow sidewalls 14a of the first heatingzone section 14. Similarly, broad walls 22b are now positionedorthogonally to broad walls 14b. The electric field distribution linesbetween the broad walls 22b indicate that the maximum intensity isprovided in the region of the narrowly spaced lines 44 while the fieldsof lower intensity are indicated by lines 46. Flange members 48 at theopposing ends of section 22 provide for mating with flange membersdisposed at the ends of transition section 34 and waveguide bend 24.Coupling apertures 50 provide for the introduction of means for securingthe mating flanges of therespective components of the waveguidetransmission structure.

It will be evident that material being heated in the first zone isexposed to an electric field pattern indicated by lines 40 and 42,extending from left to right. The same material is exposed to anelectric field distribution represented by lines 44 and 46 in thedownstream or second heating zone during the complete traversal throughthe waveguide transmission structure 2. Irregular shaped products,particularly such items as rubber molding or extrusions, which areoriginally processed from the crude rubber material in rolls may becontinuously fed into the microwave oven apparatus to be uniformly curedby exposure to such orthogonally oriented electric fields. An example ofa product of nonuniform cross-sectional configuration is shown in FIG.4. The elongated strip molding 52 comprises a plurality of hollowsections 54 and 56 within the main body 58. Such products are oftenemployed in structures to support dielectric panels within metallicchannels.

In FIG. 5, transition section 60 is provided with flange members 62 and64 and tapered waveguide sections 66 and 68 are disposed intermediatelyto the previously described rectangular waveguide heating zone sections14 and 22. In this embodiment, transition section 60 is constructed of alarger dimension hollow waveguide configuration capable of supporting,for example, microwave energy in a lower frequency range or L-band. Theadjacent mating sections 14 and 22 with the orthogonal electric fielddistributions are capable of supporting energy in a higher S-bandfrequency band. The twisting broad and narrow walls of transitionsection 34 provide for a constriction and reduction of the internalcross-sectional area available for the products to be heated. Theprovision of the larger dimensioned transition waveguide section 60permits the resultant internal access passageway to be of a largerdimension to handle larger products. The tapering waveguide sectionsprovide for the provision of a continuous path for the applied energywithin the oven apparatus. In an exemplary embodiment rectangularwaveguide, designated by the standard code WR650, has an I. D. dimensionof 6.500 for the broad walls and 3.250 for the narrow walls. The higherfrequency waveguide or S-band WR340 has I. D. dimensions of 3.400 by1.700. The tapered waveguide sections 66 and 68 are then suitablydimensioned to accommodate the mating of the respective waveguides.

In FIG. 6 a plurality of pipes 70 are shown extending through the narrowand broad walls of the waveguide sections 14, 34 and 22 comprising themain waveguide transmission structure of the oven. Fluid circulationmeans, including fans as well as plenums, are attached to these pipesfor exhausting any resultant fumes or vapors throughout the length ofthe oven. Additionally, such exhaust and circulation means can supplyany desired atmosphere within the oven to assist in the heat treatment.In the case of rubber moldings or extrusions, the circulation of heatedair removes any vapors emitted during the curing operation which maycoat the interior of the oven walls and be difficult to remove.

In FIG. 7 another variation of the invention is illustrated withparticular regard to the transition region between the orthogonalrectangular waveguides, such as section 14 and 22. A conveyor mechanism,including belt 10, is illustrated traversing an input feed structure 4joined to the outer wall of waveguide bend 16 provided for theintroduction of applied energy from the source. A resonant cavity 72defined, for example, by cylindrical walls 74, is coupled by means offlange members 76 and 78 to the waveguide sections 14 and 22. Thecircular cavity dimensions are selected to support multi-mode orthogonaldistributions of the electric fields and has, for example, an overalllength of onehalf of a wavelength of the operating frequency range of,for example, 2450 MHz. The material to be treated is transported throughthe resonant cavity by the belt with appropriate support means. Adielectric material, such as fiber glass, is preferred for the belt topermit the microwave energy to permeate the products carried by theconveyor. Numerous other resonant cavity structures will be evident tothose skilled in the art of the multimode configuration to provide forthe transition between the orthogonal electric fields in the mannerspecified in the present invention.

There is disclosed a very efficient microwave oven apparatus for theprovision of uniform heating by applied microwave energy of productshaving nonuniform cross-sectional configurations. While the inventionhas been described in a rectangular hollow conduit waveguideconfiguration, the concept is equally applicable to other transmissionstructures capable of supporting orthogonal microwave electric fielddistribution. Circular hollow waveguide or a combination of bothcircular and rectangular may be employed. Alignment problems which haveplagued processing of irregularly shaped objects, particularly those ofpoor thermally conductive materials, have been considerably reduced bythe orthogonal rotation of the electric fields with resultant uniformheating during the traversal of the product through the apparatus.

Other variations, alterations or modifications, of the disclosedapparatus will be evident to those skilled in the art. It is intended,therefore, that the foregoing description of the invention andillustrative embodiments be considered in the broadest aspects and notin a limiting sense.

I claim:

1. Microwave oven apparatus comprising:

a source of electromagnetic energy at a predetermined operatingfrequency;

a hollow waveguide transmission structure for propagating said energyand a product along a predetermined path with changing electric fielddistribution patterns of said energy as said product traverses separatesections of said structure to symmetrically heat the product;

said structure including a first waveguide section having apredetermined electric field distribution pattern and a secondwaveguidesection having the electric fields oriented orthogonally to said firstwaveguide section; and

transition means disposed between said first and second waveguidesections capable of supporting both electric field orientations.

2. Microwave oven apparatus as set forth in claim 1 wherein saidwaveguide transmission structure is of a hollow rectangularcross-sectional configuration.

3. Microwave oven apparatus as set forth in claim 1 wherein saidwaveguide transmission structure is of a hollow circular cross-sectionalconfiguration.

4. Microwave oven apparatus as set forth in claim 1 wherein saidtransition means comprise a section of hollow rectangular waveguidehaving a continuously twisting outer wall configuration.

5. Microwave oven apparatus as set forth in claim 1 wherein saidtransition means comprise a hollow circular resonant cavity.

6. Microwave oven apparatus as set forth in claim 1 wherein saidtransition means comprise a section of hollow rectangular waveguidehaving larger boundary wall dimensions relative to said first and secondzone waveguide sections.

7. Microwave oven apparatus as set forth in claim 1 wherein said energyis coupled from said source at opposing ends of said waveguidetransmission structure.

8. Microwave oven apparatus comprising:

a source of electromagnetic energy;

a hollow waveguide transmission structure for propagating said energyand a product along a predetermined path with orthogonally orientedelectric field distribution patterns of said energy in first and secondwaveguide sections during complete traversal of said product along saidpath to symmetrically heat the product;

transition means disposed between said first and second waveguidesections capable of supporting both electric field orientations; and

means for transporting the product through the waveguide transmissionstructure sections.

9. Microwave oven apparatus as set forth in claim 8 wherein saidtransportation means comprise a continuously moving belt conveyor.

10. Microwave oven apparatus comprising:

a source of electromagnetic energy;

a hollow waveguide transmission structure, for propagating said energyand a product along a predetermined path with orthogonally oriented theelectric field distribution patterns of said energy in first and secondwaveguide sections during complete traversal of said product along saidpath to symmetrically heat the product;

transition means disposed between said first and second waveguidesections capable of supporting both electric field orientations; and

means for circulating a fluid medium within the transmission structure.

1. Microwave oven apparatus comprising: a source of electromagneticenergy at a predetermined operating frequency; a hollow waveguidetransmission structure for propagating said energy and a product along apredetermined path with changing electric field distribution patterns ofsaid energy as said product traverses separate sections of saidstructure to symmetrically heat the product; said structure including afirst waveguide section having a predetermined electric fielddistribution pattern and a second waveguide section having the electricfields oriented orthogonally to said first waveguide section; andtransition means disposed between said first and second waveguidesections capable of supporting both electric field orientations. 2.Microwave oven apparatus as set forth in claim 1 wherein said waveguidetransmission structure is of a hollow rectangular cross-sectionalconfiguration.
 3. Microwave oven apparatus as set forth in claim 1wherein said waveguide transmission structure is of a hollow circularcross-sectional configuration.
 4. Microwave oven apparatus as set forthin claim 1 wherein said transition means comprise a section of hollowrectangular waveguide having a continuously twisting outer wallconfiguration.
 5. Microwave oven apparatus as set forth in claim 1wherein said transition means comprise a hollow circular resonantcavity.
 6. Microwave oven apparatus as set forth in claim 1 wherein saidtransition means comprise a section of hollow rectangular waveguidehaving larger boundary wall dimensions relative to said first and secondzone waveguide sections.
 7. Microwave oven apparatus as set forth inclaim 1 wherein said energy is coupled from said source at opposing endsof said waveguide transmission structure.
 8. Microwave oven apparatuscomprising: a source of electromagnetic energy; a hollow waveguidetransmission structure for propagating said energy and a product along apredetermined path with orthogonally oriented electric fielddistribution patterns of said energy in first and second waveguidesections during complete traversal of said product along said path tosymmetrically heat the product; transition means disposed between saidfirst and second waveguide sections capable of supporting both electricfield orientations; and means for transporting the product through thewaveguide transmission structure sections.
 9. Microwave oven apparatusas set forth in claim 8 wherein said transportation means comprise acontinuously moving belt conveyor.